The word "READER" is formed through affixation, as it is created by adding the suffix "-er" to the base word "read" to form a new word with a different meaning (a person who reads).
Affixation:
The process of adding a prefix or suffix to a base word to create a new word.
Suffix:
"-er" in this case acts as a suffix, attached to the end of "read" to indicate someone who performs the action.
